The invention relates to an inner tube element for use in a double tube device for taking soil samples during drilling operations, comprising differing end parts for coupling with several identical inner tube elements connected by a tube member made of plastic which is reinforced with fibers.
Such an inner tube element is known from European Patent Specification 0056930, of which applicants are co-owners. When a sample is wanted from a soil layer at great depth, a conventional device is used to drill through the soil layer with a core drill until the desired depth is reached. An inner tube element is pushed over the drilled core, following which the inner tube element is hoisted up and the core material is automatically retained inside the inner tube element. The string of tubes with the desired soil samples is then laid in its entirety next to the derrick and sawn there, into transportable pieces of approximately 1 meter which are closed with end caps. The sawn pieces are subsequently marked, in order to establish their relative positions. Once the tube with the core inside it is sawn it is extremely difficult to determine the vertical orientation of such a piece in the total length of the removed core, in other words, whether a certain end of such a core part is the end lying closest to the ground surface or furthest away from the ground surface. Accurate information concerning the position of such a part in the entire removed core is, of course, of vital importance for the information collected on the basis of the cores, and any doubt on the subject must be ruled out.
Attempts have been made to avoid the above-mentioned disadvantages by marking the pipes at the working site. Such operations are, however, time-consuming and expensive, and mistakes, with all their consequences, are still not ruled out.